Explosion-proof headlamp and power source



SePt- 28, 1965 w. c. MOORE ETAL 3,209,138

EXPLOSION-PROOF HEADLAMP AND POWER SOURCE Filed Feb. 5, 1962 2Sheets-Sheet l 2^ 48 42 E fg 45" 68 I NVENTORS WILLIAM CMOORE. AND BYWILUAM s. MLGRIM Mmmm Sept. 28, 1965 w. c. MOORE: ETAL 3,209,133

EXPLOSION-PROOF HEADLAMP AND POWER SOURCE Filed Feb. 5, 1962 2Sheets-Sheet 2 lll /l/ l lll VIIIIII l I N VENTORS WILLIAM C. MOOREI AND5 BYWILLIAM S. PILGRIM I; @Mww @Thx United States Patent O 3,209,138EXPLSION-PROOF HEADLAMP AND IWER SOURCE William C. Moore, Skaneateles,and William S. Pilgrim,

Port Byron, N.Y., assiguors to Welch Allyn, Inc.,

Skaneateles Fails, NX., a corporation of New York Filed Feb. 5, 1962,Ser. No. 171,048 8 Claims. (Cl. 24U-10.6)

This invention relates to explosion-proof medical head lamps and moreparticularly to a headlamp having its own connected, portable,rechargeable source of electric power in which the connecting circuit isso regulated as to prevent generation of heat suliiclient to cause anexplosion in case of a fault in the circuit in the presence of explosivegases usual to an operating room.

Explosion-proof lamps suitable for use in an explosive atmosphereusually depend on sealing the interior of the lamp from communicationwith atmosphere so that, should there be a short circuit or other faultwithin the lamp, no explosive gas can reach a spark or flame within thelamp. Such sealed lamps may be filled with an inert gas under pressureand may have, in connection therewith, a circuit breaking pressuresensitive switch or an incandescent bulb ejection device for cutting offthe electric circuit to the bulb upon the breaking of the glass of thebulb or other damage to the lamp.

Such sealed lamps are generally too heavy to be worn on a headband ifthe source of electric current is self-contained, or are inconvenientand hampering if there must be a long electrical connecting cord to aremote source of power, such as a wall plug. Moreover, ordinaryelectrical connecting cords in themselves are dangerous in that theremay be a spark or a dangerously heated area due to a short circuit orother fault in the cord sufficient to cause an explosion.

There has ,for a long time been a demand by doctors, hospitals and theirinsurers for a light-weight headlamp for use in the presence ofexplosive anaesthetic gases and adjudged safe by local regulatory rules,underwriters, and by law. The need for a source of light which may bedirected by the surgeon himself on hard-to-illuminate spots is so greatin some instances that frequently headlights that have not been approvedby regulatory agencies are being used even though the danger isrecognized.

The principal object of the present invention, accordingly, is toprovide a light-weight explosion-proof headlamp adapted to be worn on aheadband, the headlamp having its own connected source of electric powerwhich is also explosion-proof and sufficiently light-weight and rportable to be carried in a pocket or pouch supported on the person ormobilely supported nearby.

Another important object is to provide a headband-supported lamp and anindependently supported unitary battery power source which is freelyportable and rechargeable and separably connected to the lamp so as tobe easily and quickly replaceable, and which lamp, power source, andelectrical connecting means are all explosion-proof.

A further object is to provide a headeborn lamp which is easily adjustedand directed, together with a portable, rechargeable dry-cell batterypack for powering the lamp, the pack and lamp each having an explosionproof housing, and separable means electrically connecting the lamp andbattery pack in a low-voltage circuit so controlled as to be incapable,even when there is a fault in the circuit,

3,2938 Patented Sept. 28, 1965 to cause an explosion of any explosivegases which may ybe encountered in an operating room.

A still further object is to provide separate `but connectable lamp andbattery pack units, each of which is housed so as to be explosion-proof,each of which is rugged in construction, and each having the interiorthereof so closed as to suppress the propagation of llame to the outsideshould an explosion accidentally take place therein.

Other objects and advantages will become apparent from the lfollowingdescription taken in conjunction with the accompanying drawings inwhich:

FIGURE 1 is a side elevational View, partly in section on the line 1 1of FIG. 2, of a headlamp assembly according to the present invention;

FIGURE 2 is an end elevation thereof as viewed from the right of FIG. l;

FIGURE 3 is a longitudinal sectional View on the line 3 3 of FIG. 5 ofthe lamp assembly shown in FIG. l;

FIGURE 4 is a side elevational View of the male portion of the separableconnector used with the connecting cord of the headlamp assembly of FIG.l;

FIGURE 5 is an end view of the lamp assembly of FIG. 3 as viewed fromthe right;

FIGURE 6 is a top plan View on a reduced scale of the battery pack usedwith the headlamp assembly of FIG. 1, with cover removed;

FIGURE 7 is a transverse sectional View on the line 7 7 of FIG. 6; and

FIGURE 8 is a wiring diagram of the headlamp, battery pack, andconnecting circuit of the explosion proof headlamp of FIGURES l-7.

In FIGURES 1 and 2 of the drawings, a headlamp assembly 10 comprises alamp assembly 11, a socket assembly 12, and a lens holder assembly 13.

The lamp assembly 11, best seen in FIGURES 3 and 5, is provided with anincandescent lbulb 14, including a glass envelope and an incandescentfilament 16 supported within the envelope by the lead wires 17 and 18.The lead wires pass through the envelope, being sealed therein and leadwire 17 is secured by a screw 19 in electrical contact with the lampbody 2i).

The lamp body is cylindrical, hollow, and open at one end so as to beadapted to receive envelope 15 therein. The body 20 has an exteriorlythreaded annular boss 21 at its closed end and the central bore 22 ofthe boss is threaded to secure an insulating plug 23 therein. The plug23 is tubular and has a headed metal central contact member 24 extendingtherethrough, the lead wire 18 being joined lby soldering to the innerend of the contact 24. The outer end of the central contact 24 isprovided with a C-washer 25 to secure the contact in the plug 23. A setscrew 26 in the boss 21 locks the plug 23 in the bore 22 of the boss,and the incandescent bulb 14 is secured and supported within body 20 bycementitious supporting material 27 packed into the closed end of thebody.

The open end of the body Z0 is reduced in diameter to provide a shoulderat 28 and is exteriorly threaded. An interiorly threaded cap member 30is screwed to the body 20 against the shoulder 2S and is locked in placeby a set screw 29. The outer end of the cap member 30 is provided withan annular shoulder 31 about an orifice 32 and an annular lock nut 33with a similar orifice secures a glass window or plano-plano lens 34 inposition against the shoulder 31. The window 34 is sealed between nut 33and shoulder 31 as indicated at 35 as by means of an epoxy cementcapable of adhering to both glass and metal over a suitable range oftemperatures. Body 20, cap 30 and nut 33 are preferably of aluminum forstrength and lightness and the supporting material at 27, which is heatresistant, non-corrosive and a non-conductor, adheres to this metal andto the glass of envelope and hardens quickly without appreciableshrinking. The material 27 thus supports the envelope within the centralclosed chamber 36 of the lamp body, there being clearance as indicatedat 37 between envelope 15 and window 34 to allow for expansion of theenvelope when heated.

The socket or receptacle assembly 12 is best seen in FIGURE 1 andincludes a hollow receptacle body 40, also preferably of aluminum,having a cylindrical sidewall 41 and one end wall 42. Side wall 41 hasan interior diameter substantially equal to the outside diameter of thelamp body 11. The end wall has a ball post 43 secured thereto foradjustably supporting the headlamp assembly on the headband inconventional manner, and is provided in the interior of the body with aninsulating disk 44.

Telescoped within sidewall 41, an annular socket member 45 is locked inplace by a set screw 46 to divide the interior of the receptacle body 40into the terminal chamber 47 and the socket chamber 48. Socket member 45has an interiorly threaded annular sidewall portion 49 projecting towardthe open end of body 40 into which the boss 21 of lamp assembly 11 isscrewed. The socket member is also formed with a rearwardly projecting,centrally bored, end-wall boss 50 in the terminal chamber 47.

A two-piece, centrally bored, terminal Contact plug 51- 52 is secured inthe central bore of the socket member boss 50. The outer insulatingmember 51 of the plug has a shouldered head countersunk in the end wallof the socket member 45, and its other end has an enlarged bore in whichthe inner member 52 of the plug is wedged to secure the plug in thecentral bore of the boss 50. A spring contact 53, in electrical contactwith the central contact 24 of lamp 11, is secured to one end of theplug 51-52, by an electrical conductor screw 54 having a nut 55 at theother end of the plug in chamber 47, the screw 54 passing through thecentral bores of the plug pieces 51 and 52.

The sidewall 41 of chamber 47 has a passage 56 (FIG. 2) therethrough andin this passage is engaged a strain relieving nylon plug 57. One end ofan electrical connecting cord 58 is passed through the plug 57 and thelead wires 59 and 60 of the cord 58 extend into the terminal chamber 47.A terminal at the end of wire 59 is secured by the nut 55 in electricalcontact with the conductor screw 54, and the end of wire 60 is securedin electrical contact with boss 50 by the screw 61:,-

The lens holder assembly 13 comprises a sleeve member 65, a lens holderor end piece 66 and a plano-convex lens 67. The sleeve member 65 istubular and adapted to iit telescopically and slidably about the lampbody and cap member 30 to permit relative longitudinal movement forfocusing. The outer end of sleeve member 65 is internally threaded toreceive an externally threaded portion of the end piece 66.

End piece 66 is annular, having a shouldered orifice 68 axially alignedwith window 34 and lament 16. Lens 67 is secured cementitiously againstthe shoulder of the orifice 68 and a blue filter 69 may be cemented inplace adjacent the inner iat surface of the lens. The outer cylindricalsidewalls of sleeve 65, receptacle member 40, lamp body 20 and capmember 30 are grooved as shown and the parts are oxidized or anodizedblack throughout to aid in the absorption and dissipation of heat,

The connecting cord 58 is lprovided with a jack-type separableconnector, the male portion 70 of which is shown in FIG. 4. The wires 59and 60 of connecting cord 58 are connected respectively to the contacts71 and 72 at the end of jack post 73, the contacts being insulated onefrom the other in the usual manner.

The female portion 75 of the separable connector is shown in FIGURE 7connected in similar manner to another portion of the connecting cord58. It is understood that the portion 75 has a cylindrical recess 76mating with the jack post 73 with suitable insulated mating contacts atthe bottom thereof.

Referring more particularly to FIGURES 6 and 7, the battery packassembly is connected by the cord 58 to the headlamp assembly 10.

As best seen in FIGURE 7, the battery pack comprises a housing, also ofaluminum, having a receptacle portion or body 81 and a top 82, the twoparts being threadedly joined at 83 and locked in place by the set screw84 to enclose a central chamber 85. It should be noted that thisthreaded junction of the two closure parts has at least five threads inengagement when the two parts are assembled. The same live-threadedengagement of closure parts is maintained in all the threaded junctionsin the headlamp assembly 10 as well as in connection with the set screwlocking means provided with each.

The exterior of body 81 and top 82 are provided respectively with shockresisting, electrically conducting neoprene rubber covers 86 and 87cemented to their respective parts by an adhesive resistant to theliquids and gases ordinarily encountered in hospitals.

In chamber a cup-shaped power cord housing 88 of aluminum is threadedlyengaged at 89 with a suitable hole through the bottom of body 81. Thebottom of the housing 88 has an entrance passage 90 therethrough inwhich is lodged a strain-relieving nylon plug 91 at the end of theconnecting cord 58.

The wires 59 and 60 of the cord extend through the interior chamber 92of housing 88 and through an insulating bushing 93 in an annular nut 94threadedly engaged with the top end of the housing 88. Chamber 92 isclosely packed with a tire-resistant, discrete, fibrous, packingmaterial, preferably asbestos rope.

At the center of chamber 85 a cup-shaped aluminum resistor housing 95 islocated in contact with the bottom wall or iioor 96 of the receptacle orbody 81, and an axially disposed center post 97 of aluminum isthreadedly secured to the bottom of housing 95. The center post 97supports a current liming resistor 98 in the interior chamber 99 of thehousing 95 and a key 100, in appropriate slots in housing 95, post 97and resistor 98, prevents the resistor from turning with respect to thehousing. A nylon insulating sleeve 101 surrounds the resistor housingand a Teflon cover plate 102 covers the housing inside the sleeve.Appropriate registering holes are provided in sleeve 101 and housing 95for the hereinafter described connecting wires to the resistor 98,

Disposed around the resistor housing 95 on either side of the power cordhousing 88 are five rechargeable drycell batteries 103, preferably ofthe nickel-cadmium type. The batteries are connected in series byconnecting wires 104 as shown, it being understood that alternatebatteries are inverted so that each battery is connected at the top tothe battery on one side and at the bottom to the battery on the otherside. Annular grooves 105 and 106 are provided in the bottom Wall 96 ofthe body and the underside of top 82 to provide space for the connectingwires 104. The connecting cord lead wire 59 and resistor 98 are alsoconnected in the series circuit with batteries 103, wire 59 beingconnected to the resistor and wire 60 being connected to one of thebatteries, as shown.

Insulating strips 107 of paper or other suitable material are provided,as best shown in FIG. 6, to separate adjacent batteries and a sleeve 108of similar material is provided for housing 88. Shock-absorbing disks109 and 110 of sponge rubber are provided between the batteries and vthe bottom 96, and a similar hole is provided for housing 88.

It will be noted that the batteries 103 are rmly held in place by thesponge rubber padding 109, 110, 111, and the batteries and housings 88and 95 are compactly arranged in chamber 85 so as to leave a minimum ofempty space within the pack 80. The batteries shown each have a ratedVoltage of less than a v-olt and a half. Resistor 98 has a similar lowrating of 1.3 ohms for a 5 watt light source and limits the currentavailable in the low voltage connecting circuit shown in FIGURE 8 incase of a short circuit or other fault.

It will also be understood that larger batteries may be similarly usedin an enlarged or heavier pack to give longer life between rechargings,but the same low voltage and restriction in the current available may bemaintained. `Such larger packs are more conveniently supported behindthe user on a mobile stand, such as an infusion stand which is readilyavailable in hospitals. The smaller and lighter pack 80, however, isadapted to be carried in a pocket, or in a pouch strapped around thewaist of the user.

In operation the pack is carried in any convenient manner and theheadlamp assembly :10 is worn on a headband. To turn the lamp on, theparts 70 and 7S of the separable connector are joined. Current Hows fromthe batteries 103 through resistor 98 and the connecting circuit to theincandescent bulb 14. Light from the lilament -16 may be concentrated atany desired distance from the headlamp by moving the lens holderassembly telescopically to carry lens 67 away from or toward the window34 in the usual manner.

The headlamp 10 is of very rugged construction and has la minimum ofunoccupied space therein. The incandescent :bulb 14 is firmly supportedin the chamber 36, but should the glass envelope 15 :be shattered, forany reason, the still glowing iilament 16 is completely enclosed in thechamber 36.

No attempt has been made to pressurize this chamber or to seal it orchambers 47 and 48 with high pressure seals to make them vapor proof.The threaded connections between the component parts of the headlamp andpack assemblies may be pervious to explosive gases, as are the powercord entrances to the receptacle 12 and pack housing 81-82 which arerespectively engaged by the nylon plugs 57 and 91.

Chamber 36, however, is provided at one end with the comparatively thickglass window 34 sealed at 35 to the cap 30. Moreover, chamber 36 issurrounded, at this end, by the sleeve 65 and associated parts.

At the other end of chamber 36 the socket chamber 4S enclosing contacts53 and 24 communicates with the lirst chamber 36 only along the tightlytting insulating plug 22 and the inner end of the plug is sealed by thecovering of cementitious supporting material 27. The chamber 47, inwhich the terminal ends of wires 59 and 6@ are contained, is not sealedbut its entrance passage supports the strain relieving plug 57.

Should explosive gases seep into the comparatively small unoccupiedspace in chamber 36 and an explosion occur therein, the walls of thechamber are amply strong to contain the explosion as has beendemonstrated by test. The devious and tortuous minute passages along thethreaded connections or between the tightly fitting parts between thechamber 36 and the exterior of the headlamp assembly suppress anypropagation of liame outside the headlamp.

The interior chamber 85 of the battery pack 80 is also screened fromdirect communication with an explosive atmosphere outside the pack.Communication from chamber -85 to the exterior of the pack housing isonly along the threads at 33, or along the threaded junction 89 betweenthe cord housing 88 and the bottom wall 96, or through housing 88 andpast the plug 91 in passage 91B. This last mentioned path, of course, isthrough the tightly packed asbestos rope at 92. Any of the paths ofcommunication between the chamber and the outside of the pack is thusalong a tortuous and devious route between closely fitting particles orwalls which suppress the propagation of tflame from within the batterypack.

The low voltage connecting circuit between batteries 103 and lament 16has the current limiting resistor 98 wires in series therein. Should thecord 58 become worn or short circuited the current is limited by theresistor, preventing even an instantaneous surge, and the heat which canbe produced by a fault in the cord 58 is limited to an amount well underthat required to ignite the anaesthetic gases ordinarily encountered.

Both `battery pack and headlamp assembly are sufiiciently rugged inconstruction to meet the strictest underwriters tests for accidentalbreakage and are designed for rapid heat dissipation. The blackcoloration and grooved outer surfaces of the headlamp assembly collectand dissipate the heat so that the exterior surface may be comfortablyhandled even after extended use. In the pack 80, the housing in itsnylon sleeve acts as a heat sink for the resistor 98. Should theresistor become overheated because of a short circuit, the post 97carries the heat freely to the bottom of housing 95 and thence to thebottom 96 of the pack housing to dissipate the heat throughout theentire housing.

It will be apparent that by providing the separable connector 70, 7Sbetween pack and lamp, the need for a switch is eliminated and alsomeans are provided for removing a pack which has become exhaustedthrough use and substituting another fully charged pack. The pack whichhas been removed may then be recharged by plugging its connector 75 intoa battery charger provided with a connector pack-post similar to thatshown at 73, FIGURE 4.

[As will be apparent to those familiar with the art, the invention can:be embodied in other specific forms without departing from the spiritor essential characteristics thereof. The embodiment disclosed istherefore to be considered in all respects as illustrative rather thanrestrictive, the scope of the invention being indicated by the appendedclaims.

What is claimed is:

1. An explosion-proof headlamp having its own connected source ofelectricity and adapted to be worn in an explosive gas atmosphere,comprising: a light-weight lamp assembly having a rst closed chamber anda second chamber having threadedly interengaged walls, said rst chamberhaving a sealed transparent window in one wall thereof, a sealed glasslamp envelope supported in the iirst chamber and having a filament andexterior lead wires connected to the filament, a pair of terminalssupported in the second chamber, current carrying means connecting theterminals to the lead wires with at least one such means being insulatedin the wall bet-Ween said chambers; a battery pack assembly havingthreadedly engaged housing parts deiining a central closed chamber, aplurality of low-voltage rechargeable dry type battery cells and adischarge current limiting resistor mounted in said central chamber; andinsulated current conducting means including a ilexi'ble cord connectingsaid terminals and said batteries and resistor in a low-voltage seriescircuit, said second chamber and said central chamber having entrancepassages for said cord, a resilient strainrelieving plug around the cordat each of said entrance passages, and discrete non-inflammable iibrouspacking material around the cord in said central chamber entrancepassage, whereby current is limited in said cord lfor preventingoverheating in case of a fault in the cord, and said first chamber isclosed to suppress the propagation of any flame therein to the outside.

2. An explosion-proof head1-amp adapted for use in an explosive gas`atmosphere comprising: a tubular closed walled chamber having a sealedtransparent window forming one end wall thereof; a sealed glass envelopein said chamber; an incandescent ilament in said envelope; lead wiresextending from said iilament through said glass envelope; a tirstinsulated contact in the other end wall of said chamber and connected toone of the lead wires; cementitious material supporting said glassenvelope in the chamber; a second walled chamber having therein a secondinsulated contact in resilient connection with said rst contact; a thirdwalled chamber having therein a rst terminal secured in electricalcontact with said second insulated contact and a second terminalelectrically connected to the other iilament lead wire, one wall of saidthird chamber having an entrance passage therethrough; a resilient plugengaged in said passage, and a pair of insulated wires each connected toa respective one of said terminals passing through said plug forconnecting said lilament with a source of electric current.

3. The headlamp of clai-m 2 having a tubular sleeve telescopicallyengaged about one end thereof, said sleeve having a shouldered orificeat one end aligned with said transparent window and lament, and aplano-convex lens secured in said orice against the shoulder forfocusing light from the iilament by moving said sleeve telescopically.

4. An explosion-proof medical headlamp adapted to be worn on a headband,comprising: a hollow supporting base portion having a cylindricalsidewall and one wall adapted to be secured to the headband; saidsidewall having a passagetherethrough; a resilient plug engaged in saidpassage; an electrical connecting cord adapted to be connected to asource of electric current and having one secured in said plug; anannular metal socket member telescopically fitted and secured withinsaid base portion and dividing the interior thereof into a terminalchamber and a socket chamber; said cord having wires extending into saidterminal chamber; an axially extending bore through said socket member;an axially bored insulator plug in said socket member bore; a springcontact at one end of said insulator plug; electrically con- V/ductivemeans through said plug bore securing said spring contact to one end ofthe plug and one of said Wires to the other end of the plug; the otherwire being secured in electrical contact with the socket member; saidsocket member having an annular internally threaded sidewall extendingaxially away from said spring contact member; a cylindrical metal lampbody having an annular boss at one end threadedly engaged within saidinternally threaded sidewall; said lamp boss having a threaded centralbore therein; a tubular insulator threadedly engaged in said centralbore; a metal center contact secured Within said tubular insulator andhaving one end in contact with said spring contact; a lamp including aglass envelope, a filament sealed in the envelope, and lead wiresextending from the li'lament outside the envelope; one lead wire beingsecured in electrical contact with said lamp body and the other leadwire being secured in electrical Contact with said center contact;cementitious supporting material securing said lamp envelope Within saidlamp body; a cylindrical hollow lamp top cap threadedly engaged at oneend with said lamp body and having a shouldered oriice at the other end,set screw means locking said top cap and lamp body in engagement, anannular nut threadedly engaged within said top cap, and a glass windowsecured between said shouldered oriiice and said annular nut andcementitiously sealed therebetween, whereby said lamp is enclosed forpreventing the propagation of a llame outside of said headlamp.

5. An explosion-proof battery pack adapted to be carried in a pouch andconnected for use with a medical headlamp in an explosive gasatmosphere, comprising: la metal housing having two threadedly engagedportions defining a central closed chamber, a plurality of rechargeablesealed, dry type battery cells and discharge current limiting meanspositioned in said chamber, an entrance passage tothe chamber in saidvhousing,- a connecting oord adapted to be connected to the headlampandphaving a resilient plug at one end engaged in said passage, saidcord having wires extending into said chamber and connecting saidbattery cells and current limiting means in series, and discretenon-iniiammable iibrous material packed in said passage about said Wireswhereby the propagation of any flame in the chamber to the outside issuppressed.

6. An explosion-proof battery pack adapted for use with a medicalheadlamp in an explosive atmosphere, comprising: a hollow metal bodyhaving a receptacle portion and a cover portion threadedly interengagedto provide a closed body chamber; means for locking said receptacle andcover portions in engagement; a plurality of dry rechargeable batteriesand a discharge current-limiting resistor disposed within said bodychamber and connected in series; an entrance chamber within said bodychamber having a passage at one end leading outside said body andcommunicating at its other end with said body chamber; a connecting cordhaving one end adapted to be connected to the headlamp and havingelectrically conductive wires at its other end leading through saidpassage and said entrance chamber and being connected in said bodychamber to said batteries and resistor; and discrete noninflammableliibrous packing material in said entrance chamber tightly packed aboutsaid wires; whereby communication from the interior of said body chamberto the atmosphere is so minutely tortuous and devious as to suppresspropagation of liame from said body chamber to the explosive atmosphere.

'7. The battery pack of claim 6 having conductive, resilient,shock-absorbent covering material adhesively secured to the outersurfaces of said metal body, and having a lining of soft and resilientinsulating material disposed between the walls of said body chamber andsaid batteries, whereby injury to said body and its contents isprevented if the pack is accidentally dropped.

8. An explosion-proof battery pack adapted to be carried in a pouch andconnected for use with a medical headlamp in an explosive atmosphere,comprising: a hollow metal body having a receptacle portion and a coverportion threadedly interengaged to provide a cylindrical closed chamber;set screw means for llocking said receptacle and cover portions inthreaded engagement; a layer of electrically conductive, resilient,shock-absorbent material adhesively secured to the outer surfaces ofsaid body; a layer of soft resilient electrical insulating materialdisposed about the walls of said closed chamber, a cylindrical hollowpower cord housing in said chamber threadedly secured at its outer endto said body; an entrance passage through said body into said cordhousing; a resilient plug in said passage; a power cord having one endpassing through the plug and being adapted at the other end forconnection to said headlamp, said cord having electrically conductivewires extending into said chamber through said housing; asbestos rope insaid housing packed about said wires; a hollow cylindrical resistorhousing in contact with said body and centrally disposed in saidchamber; a discharge current limiting resistor secured within saidresistor housing; an insulating sleeve about said resistor, said sleevehaving a cover therefor; and a plurality of rechargeable cylindricalbattery cells disposed in said chamber about said resistor housing oneither side of said power cord housing so as to substantially fill saidchamber; said cells and said resistor being connected in a seriescircuit with said power cord wires for illuminating said headlamp, saidresistor housing and sleeve having passages therethrough for saidconnection, whereby current through said cord is limited to generateless heat than needed to ignite the explosive atmosphere in case of afault in the cord, and said entrance passage for the cord is so tortuousand devious by reason of said asbestos packing as to suppresspropagation of a llame from Within said chamber to the explosiveatmosphere.

References Cited by the Examiner UNITED STATES PATENTS Wappler 240-1066Yost 240-112 Wheat 240-106 Watkins 240-10.6 10 Blood 240-11.2

Merrill 24U-10.6 Arnesen 128-23 Gellman 12S-22 McNail 240-10.6 Muller240-10.61 Werner 24U-10.6 Font 174-52 Amlee 240-52 Monroe 24U-123 XNORTON ANSHER, Primary Examiner.

1. AN EXPLOSION-PROOF HEADLAMP HAVING ITS OWN CONNECTED SOURCE OFELECTRICITY AND ADAPTED TO BE WORN IN AN EXPLOSIVE GAS ATMOSPHERE,COMPORISING: A LIGHT-WEIGHT LAMP ASSEMBLY HAVING A FIRST CLOSED CHAMBERAND A SECOND CHAMBER HAVING A SEALED TRANSPARENT WINDOW IN ONE FIRSTCHAMBER HAVING A SEALED TRANSPARENT WINDOW IN ONE WALL THEREOF, A SEALEDGLASS LAMP ENVELOPE SUPPORTED IN THE FIRST CHAMBER AND HAVING A FILAMENTAND EXTERIOR LEAD WIRES CONNECTED TO THE FILAMENT, A PAIR OF TERMINALSSUPPORTED IN THE SECOND CHAMBER, CURRENT CARRYING MEANS CONNECTING THETERMINALS TO THE LEAD WIRES WITH AT LEAST ONE SUCH MEANS BEING INSULATEDIN THE WALL BETWEEN SAID CHAMBER; A BATTERY PACK ASSEMBLY HAVINGTHREADEDLY ENGAGED HOUSING PARTS DEFINING A CENTRAL CLOSED CHAMBER, APLURALITY OF LOW-VOLTAGE RECHARGEABLE DRY TYPE BATTERY CELLS AND ADISCHARGE CURRENT LIMITING RESISTOR MOUNTED IN SAID CENTRAL CHAMBER; ANDINSULATED CURRENT CONDUCTING MEANS INCLUDING A FLEXIBLE CORD CONNECTINGSAID TERMINALS AND SAID BATTERIES AND RESISTOR IN A LOW-VOLTAGE SERIESCIRCUIT, SAID SECOND CHAMBER AND SAID CENTRAL CHAMBER HAVING ENTRANCEPASSAGES FOR SAID CORE, A RESILIENT STRAINRELIEIVING PLUG AROUND THECORE AT EACH OF SAID ENTRANCE PASSAGES, AND DISCRETE NON-INFLAMMABLEFIBROUS PACKING MATERIAL AROUND THE CORD IN SAID CENTRAL CHAMBERENTRANCE PASSAGE, WHEREBY CURRENT IS LIMITED IN SAID CORD FOR PREVENTINGOVERHEATING IN CASE OF A FAULT IN THE CORD, AND SAID FIRST CHAMBER ISCLOSED TO SUPPRESS STHE PROPAGATION OF ANY FLAME THEREIN TO THE OUTSIDE.